Heat stock in a saucepan and keep warm
Sauté mushrooms in butter until golden, set aside
In the same pan, cook onion until soft
Add garlic and cook briefly
Stir in Arborio rice and toast lightly
Add warm stock one ladle at a time, stirring constantly
Let liquid absorb before adding more stock
Continue until rice is tender and creamy
Stir in cooked mushrooms
Remove from heat and finish with butter and Parmesan